[16] Glycerol is primarily made as a by-product of biodiesel production.
Biodiesel is produced using trans-esterification, which is a chemical reaction involving vegetable oil or animal fat and a monovalent alcohol (usually methanol). This process makes crude glycerol which must be purified before it can be used for most applications. There is 10 wt% glycerol produced from the reaction, with the rest being biodiesel. In 2008, the total production of glycerol was estimated to be 1.224 million metric tonnes, and the total demand was approximately 0.9 million metric tonnes [23]. The amount of biodiesel being produced is rapidly rising, so there will be more and more glycerol being made, which should be taken advantage of considering its wide variety of applications.
The conventional method uses KOH as a catalyst, but this is toxic and must be removed afterwards. The crude product that is produced from the conventional method contains triglycerides, alcohol, glycerol, biodiesel, soaps and contaminants. [13]
In recent years, scientists have been developing a new method for producing glycerol and biodiesel, by using heterogeneous catalysts (enzymes) instead of a homogenous catalyst.
The types of enzymes that are currently used most often are lipases. The enzymes must be immobilized for best results. When this method is used almost all of the triglycerides and alcohols are converted. This results in much less waste products, especially soaps, making the process much more environmentally friendly. It also cuts down on the purification costs and energy requirements because the crude glycerol and biodiesel produced are much more pure.
Some drawbacks are:
it’s more time consuming than the conventional method
the enzymes have a limited number of reuses
certain conditions must be to keep the enzymes active and immobilized
Enzyme immobilization Immobilization of enzymes is a process that causes enzymes to become stuck to a solid surface, while still active. It is currently carried out using the following three methods: 1) Adsorption onto a solid support 2) Covalent bonding to a solid support 3) Trapping of enzymes on a polymer matrix support
The use of a polymer matrix to trap the enzymes is the preferred method because it gives the highest enzyme activity and stability. Advantages of enzyme immobilization include: 1) The enzymes don’t contaminate the biodiesel and glycerol, since they can be removed from the mixture still attached to the support 2) The immobilization tends to make the enzymes more active, therefore the process can be completed faster and more of the desired end products are produced 3) The enzymes can be recycled and used many times
Factors affecting enzyme activity and trans-esterification Ideally, the methanol concentration should be kept below one third the stoichiometric amount. When this is done, it results in complete conversion of the methanol. If there is too much methanol, the enzymes become inactive and can’t be used again. Therefore, the process is usually done in several steps, where each time the desired products are separated and sent for storage, and more methanol is added. A water concentration above 500 ppm decreases the trans-esterification process. Glycerol lowers the enzyme activity, so it must be quickly removed to give the highest yields and the most reuses of the enzymes. The pH and temperature of the mixture must be kept within a certain range for maximum enzyme activity and adhesion to the solid supports. The required range is dependent on the types of enzymes used.
What makes the production process green? 1) The process uses renewable resources (vegetable oil and alcohol) 2) Complete conversion of alcohol and triglycerides is possible by using enzymatic trans-esterification 3) The conversion of all the fats means soaps, which are harmful to the environment, do not form in the waste oil 4) Energy requirements for refining are low since the crude glycerol is quite pure
The Making of Glycerol
[16]
Glycerol is primarily made as a by-product of biodiesel production.
Biodiesel is produced using trans-esterification, which is a chemical reaction involving vegetable oil or animal fat and a monovalent alcohol (usually methanol). This process makes crude glycerol which must be purified before it can be used for most applications. There is 10 wt% glycerol produced from the reaction, with the rest being biodiesel. In 2008, the total production of glycerol was estimated to be 1.224 million metric tonnes, and the total demand was approximately 0.9 million metric tonnes [23]. The amount of biodiesel being produced is rapidly rising, so there will be more and more glycerol being made, which should be taken advantage of considering its wide variety of applications.
The conventional method uses KOH as a catalyst, but this is toxic and must be removed afterwards. The crude product that is produced from the conventional method contains triglycerides, alcohol, glycerol, biodiesel, soaps and contaminants.
In recent years, scientists have been developing a new method for producing glycerol and biodiesel, by using heterogeneous catalysts (enzymes) instead of a homogenous catalyst.
The types of enzymes that are currently used most often are lipases. The enzymes must be immobilized for best results. When this method is used almost all of the triglycerides and alcohols are converted. This results in much less waste products, especially soaps, making the process much more environmentally friendly. It also cuts down on the purification costs and energy requirements because the crude glycerol and biodiesel produced are much more pure.
Some drawbacks are:
Enzyme immobilization
Immobilization of enzymes is a process that causes enzymes to become stuck to a solid surface, while still active. It is currently carried out using the following three methods:
1) Adsorption onto a solid support
2) Covalent bonding to a solid support
3) Trapping of enzymes on a polymer matrix support
The use of a polymer matrix to trap the enzymes is the preferred method because it gives the highest enzyme activity and stability.
Advantages of enzyme immobilization include:
1) The enzymes don’t contaminate the biodiesel and glycerol, since they can be removed from the mixture still attached to the support
2) The immobilization tends to make the enzymes more active, therefore the process can be completed faster and more of the desired end products are produced
3) The enzymes can be recycled and used many times
Factors affecting enzyme activity and trans-esterification
Ideally, the methanol concentration should be kept below one third the stoichiometric amount. When this is done, it results in complete conversion of the methanol. If there is too much methanol, the enzymes become inactive and can’t be used again. Therefore, the process is usually done in several steps, where each time the desired products are separated and sent for storage, and more methanol is added. A water concentration above 500 ppm decreases the trans-esterification process. Glycerol lowers the enzyme activity, so it must be quickly removed to give the highest yields and the most reuses of the enzymes. The pH and temperature of the mixture must be kept within a certain range for maximum enzyme activity and adhesion to the solid supports. The required range is dependent on the types of enzymes used.
What makes the production process green?
1) The process uses renewable resources (vegetable oil and alcohol)
2) Complete conversion of alcohol and triglycerides is possible by using enzymatic trans-esterification
3) The conversion of all the fats means soaps, which are harmful to the environment, do not form in the waste oil
4) Energy requirements for refining are low since the crude glycerol is quite pure
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